The need for improved food preservation methods is great. It has been estimated that a large part of the world's food supply is lost as a result of microbial spoilage and food-borne microbial infections represent a constant and serious threat to human health.
Several bacterial species that may contaminate and grow in foodstuffs and crops are pathogenic or produce toxins and cause a range of food-poisoning diseases. Despite substantial improvement in the technology and hygiene, food products may be exposed to spoilage and pathogenic bacteria in the food-handling environment and the number of food poisonings is still increasing in most of the countries. Food preservation techniques, e.g. heat processing, freezing, ultrasound, irradiation, and high pressure treatment, significantly reduce microbial load but of particular concern is the evidence that processed foods are contaminated with micro-organisms following processing and prior to packaging. Of rising concern in the food industry are microbial problems related to various foods such as dairy and meat products, fresh and chilled foods and seafood.
Especially food products in the pH range of 4.5 to 7.0 are known to be susceptible to microbial spoilage by micro-organisms, including pathogens and spore forming bacteria. At lower pH levels, yeasts, moulds and acid-tolerant bacteria are most relevant. Mostly, processed foods are not consumed directly after processing, thereby permitting bacteria surviving the production process or introduced by post-contamination to grow. Since food consumption may occur without reheating the processed foods to sufficient temperatures for sufficient time, there is a risk of food poisoning or food spoilage.
Furthermore, the recent trend for minimally processed foods with the intrinsic nutritional and sensory qualities of raw and fresh foods has raised the safety risk. Milder preservation treatments, such as high hydrostatic pressure and pulsed-electric-field techniques have proven to be successful, but often rely on effective hurdles, i.e. cold chain and addition of natural antimicrobials.
There has been extensive research conducted in the field of food safety to develop effective anti-microbial product designs, which result in a combination of compositions, processing and shelf-life conditions.
Nisin is a peptide-like antibacterial substance produced by Lactococcus lactis subsp. lactis. It comprises 34 amino acids and is active against mainly gram-positive bacteria. Nisin is non-toxic and is free of side-effects. Nisin is a Generally Recognized as Safe substance and is widely used in a variety of foods. Examples of such products are processed cheese, milk, clotted cream, dairy desserts, ice cream mixes, liquid egg, hot-baked flour products, dressings and beer. Nisin is heat-stable and survives pasteurisation temperatures with minimal loss of activity.
Usually, nisin is obtained by fermentation of a species of Lactococcus lactis and is further formulated as a dry powder that can be used as a preservative as such or after having first being solved into a suitable solvent. Delvoplus® and Nisaplin® are brand names for a nisin powder containing 1 million IU per gram. They are distributed by DSM and Danisco, respectively. These powdered nisin products have several drawbacks: dust is generated upon handling, and dosing and mixing small amounts of powders into products is difficult. Therefore, liquid nisin compositions which do not have the drawbacks described above are commercially preferred.
Liquid nisin compositions as such are known in the art. Although liquid nisin compositions have been reported to have activity against gram-positive bacteria (see Mota-Meira et al. (2000), Montville et al. (1999), U.S. Pat. No. 5,584,199 and U.S. Pat. No. 4,597,972) and even gram-negative bacteria (see EP 0 453 860, U.S. Pat. No. 5,260,271 and U.S. Pat. No. 5,559,096), there is still a need for liquid nisin compositions having an improved antimicrobial activity, particularly against gram-positive bacteria found in the food industry.